CBR 125 Front brake problems

[BillyJ]

So my CBR was fine before winter,
it's now been sitting in my garden for about a week and i found out today that the front bake is showing very odd behavior...
when the handle bars are center or full lock left, the brake behaves as you would expect... not braking till you pull the lever... but when you turn the handlebars to full lock right, the front wheel for some reason locks up as if the lever was being pressed??

I've had a look at the line and it doesn't seem to be pinched anywhere..


WHY

[Robby]

I've had a think about this since having a look at it. The first thing to do is work out if the problem is down to the brake, or down to something else.

To do this, you need to get the brake caliper pistons pushed back in so the pads aren't dragging on the disc. Your pads are knackered, so the easy way to do this is to carefully get a flat-bladed screwdriver between the pads and disc, and gentle push the pistons back in with it.

Now that the caliper isn't dragging, try moving the bike back and forth to see if it makes a difference. Don't touch the brake at this point.

If this sorts it, but pumping the brake back up makes the problem return, then I need to think more. If I feel charitable I'll come round with tools and sort out some bits on the bike in the next couple of weeks.

[BillyJ]

ok ill have a look later,
but i was thinking it could of been the chain tension? but then the wheel locked up and dragged, so maybe not, ill force them apart this evening and let you know.

Thank you!

[BillyJ]

so i stuck a screw driver in there and separated the pads when the bars where at right lock,
the wheel moved fine there was still a bit of friction but that was probably just me not fully separate them?

anyway, when i went to pull in the brake lever, still at full right lock, the lever pulled in further then normal then after a couple of squeezes it went back to a short pull and the wheel would lock up again?

[Robby]

I've been turning this over in my head for a few days, there must be a problem at the master cylinder.

The solution is to get the thing apart and clean it. If the brake fluid has never been changed, then it's 5-6 years old and there could be some contamination in there.

I'm available on friday this week, and either saturday or sunday, so if you're about I can come over then and have a look. Get a can of brake cleaner, I want to clean the piston on the 250 caliper as well. If you order some pads for the 125 I'll change them as well. I'll even have a go at your ignition.

[krarkol]

The brake only needs to be on slightly for the front wheel to lock when stationary.

My guess is that as the brake lines moving, it is somehow pushing the master cylinder or pulling the piston near the lever. But only slightly so barely noticeable when just looking at the lines
____________________
Bandit 600 - deaded

[nightshaddow]

robby seems to know what he is doing but the obvious things to check are kinked/squashed brake lines

if it was me i would strip and rebuild the whole braking system and rebuild it replacing anything that looked suspisious
____________________
"WHAT DO YOU MEAN 100 MPH THATS IMPOSSIBLE Its chinese OFFICER."
Current rides CB 125 TDE(the next project) NS125RK ( now on the road ) CB125TDC (soon to be project 17) melody ( the nephews )

[BillyJ]

ok, so i can get a pair of (front and rear) pads for £25 but they might not come till monday next week, ill message them to ask about express delivery, and what kind of fluid should i get for the brake lines, and Robby, sunday would be great!

Thanks guys

EDIT: All of the weekend is good, but what time?

[Robby]

I'm going to be busy on either saturday or sunday, probably sunday, will try to find out today.

For brake fluid you want either DOT4 or DOT5.1, NOT DOT5. Get whatever is cheapest from your local garage, it all does the same thing.

Try to get some new copper washers too. A bike shop will well them, I only need 4 but try to get 10, always worth having spares on the shelf. They're a standard size, just ask for copper washers for brake lines.

Try to get some latex or nitrile gloves too. Brake fluid is nasty stuff.

To answer some of the questions from other people in the thread:

1. The brake lever isn't touching on anything, and the line isn't being squeezed anywhere.
2. The bike has been down the road at some point, there's a little scuffing on the master cylinder lid.
3. There is no suggestion of a prior brake fluid change, and the bike is a 2007 model.

I'm clutching at straws somewhat, but some remote possibilities are:
1. General crap in the fluid is blocking the master cylinder fluid return hole when the bars are moved around to the right.
2. An air bubble is exerting a tiny amount of pressure somewhere.
3. The old fluid has absorbed enough water to have too much fluid in the system, exerting pressure at odd times.

My plan is to drain down the system, clean the caliper and master cylinder fully, give it all a proper visual inspection, and reassemble. I'll have a look at the ignition switch while I have it all apart - its wiring appears to have been routed incorrectly.

[BillyJ]

in the next few days, the lovely post man should bring me:
front and rear pads for my cbr
a liter of brake fluid
and some autosol for the cb 250 rims,

i'm looking at crush washers, but there are a few sizes, either m8, m10 or m12.
im assuming m10 because it comes up slightly more often, could someone confirm this for me its a cbr 2006 model by the way

[Robby]

I'm not sure what size the washers are, but look for brake banjo bolt crush washers, they're a standard size. Probably M10.

[BillyJ]

I have everything we need then, but some of it wont come until Monday, so do you want to wait until next weekend after this one to have a look?